What is the function of encounter patterns in ant colonies?

Abstract

Abstract. This study explores how patterns of brief antennal contacts may function in the organization of ant colonies. In the course of antennal contact, an ant can determine whether another is a nestmate. The first part of the work was comparative, and showed that three ant species (Solenopsis invicta, Myrmica rubra, and Lasius fuliginosus) differ in the frequency, location and context of antennal contact. The next part examined whether ants might use the rate of contacts with nestmates as a cue to nestmate density. Density was varied experimentally, and variation in contact rate was measured. If encounters between ants were the result of purely random collisions, the principles of Brownian motion suggest numbers of contacts would increase quadratically with numbers of ants. The results show that in undisturbed conditions, contact rate was not random. Instead ants (L. fuliginosus), regulated contact rate. Ants aggregated more when density was low, which keeps contact rate up, and avoided contact with nearby ants when density was high, which keeps contact rate low. One ant responds to another, and thus can decide whether to engage in contact, at a distance of 1 · 2 cm. Next, ants were exposed to workers from another colony. In these disturbed conditions, contact rates increased. The magnitude of the increase depended on proportions, not numbers of non-nestmates present, suggesting that contact rate may be a cue to nestmate density.